1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly to a method for recovering from a multimedia broadcast/multicast service (MBMS) data reception error.
2. Description of the Related Art
Multimedia broadcast/multicast service (MBMS) is a method for providing a multimedia service to user equipments (UEs) subscribed to the service through a single channel in a wideband code division multiple access (WCDMA) system. MBMS is characterized in that the method can maximize the efficiency of channel use as two or more UEs share and receive the single channel, provide the multimedia service while efficiently using the channel, and provide high quality service at low cost.
FIG. 1 is a schematic block diagram illustrating a process by which the MBMS is applied to a radio mobile communication network. The MBMS will be described in detail with reference to FIG. 1. FIG. 1 illustrates a plurality of user equipments (UEs) 101-108, a Node-B 121, a radio network controller (RNC) 131, and a core network (CN) for controlling or providing the MBMS. The UEs capable of receiving the MBMS include a 1st UE 101 to an 8th UE 108. Some of the UEs are included in one a plurality of cells. The 1st UE 101 to 3rd UE 103 are included in a 1st cell 111, and the 4th UE 104 and the 5th UE 105 are included in a 2nd cell 112. The MBMS in the cells is supported by a Node-B 121. For the convenience of explanation, the Node-B is explained using a cell concept. It is obvious that the Node-B can manage one cell or a plurality of cells. For illustrative purposes, in FIG. 1, the Node-B 121 manages three cells 111-113. The RNC 131 receives packet data (multimedia data) from a serving general packet radio service (GPRS) support node (SGSN) 141 and then supports or delivers the MBMS to the specified Node-B 121. Furthermore, the RNC 131 controls radio channels between the Node-B 121 and the UEs 101 to 108 to provide the MBMS. The RNC 131, the Node-B 121, and the cells 111 to 118 constitute a universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN), and the UTRAN connects the UEs to the CN.
The SGSN 141 controls an MBMS-related service for subscribers. For example, the SGSN 141 manages context information relating to the MBMS. For this, the SGSN 141 must recognize a list of RNCs 131 receiving the MBMS. Further, the RNC 131 controls the cells, and delivers service data to a cell desiring to receive the MBMS among the cells managed thereby. The SGSN 141 connected to a home location register (HLR) 151 performs a subscriber authentication procedure.
A gateway GPRS support node (GGSN) 161 receives MBMS data to be supplied to the UEs 101 to 108 supporting the MBMS from a contents provider 191 and multicast broadcast sources 192 and 193 through a broadcast/multicast service center (BM-SC) 181 and a border gateway (BG) 171 and then transmits the received MBMS data to the SGSN 141. Further, the GGSN 161 manages movement state information of the UEs 101 to 108 and also manages service quality of the received MBMS. The BG 171 receives MBMS data from the multicast broadcast source 192 that is located in a network not currently managed by a service carrier and then transmits the received MBMS data to the GGSN 161. The BM-SC 181 receives the MBMS data from the contents provider 191, transfers the received MBMS data to the GGSN 161, and simultaneously performs an authentication function relating to the contents provider 191, an MBMS quality decision function, an error correction function relating to MBMS data loss, a billing function relating to contents supply, and a notification function relating to the MBMS currently provided to the UEs 101 to 108. The contents provider 191 and the broadcast multicast sources 192 and 193 are MBMS data sources.
As described above, an MBMS data stream is delivered from the contents provider 191 to the GGSN 161 through the BM-SC 181 or from the multicast broadcast source 192 to the GGSN 161 through the BG 171, or is directly delivered from the multicast broadcast source 193 to the GGSN 161. The GGSN 161 transfers the received MBMS data stream to the UEs 101 to 108 through the SGSN 141 and the RNC 131.
In order for an arbitrary MBMS service to be provided, basic information relating to the MBMS service must be provided to the UEs so that an arbitrary MBMS service can be provided where the UEs desire to receive the arbitrary MBMS service, and a list of the UEs must be transferred to the network. When receiving the list of the UEs requesting the arbitrary MBMS service, the network must page the UEs and set up a radio bearer for providing the MBMS service. After the radio bearer is set up in relation to the UEs, the arbitrary MBMS service is provided through the radio bearer. However, if the MBMS service has been terminated, the UEs must be notified of the fact that the MBMS service has been terminated. At this point, all UEs must release all resources assigned for the MBMS service.
FIG. 2 is a flow chart illustrating a process for performing the MBMS service between the conventional RNC and UEs requesting the service. The MBMS service is provided to corresponding UEs requesting the service via the Node-B by the RNC. However, the Node-B is not shown in FIG. 2, but it is obvious that the MBMS service is provided via the Node-B. Further, the CN illustrated in FIG. 2 also includes the SGSN, GGSN, BG, contents provider, BM-SC, etc.
UEs (UE #1, UE #M, and UE #N) 201 to 203 illustrated in FIG. 2 request a corresponding MBMS service, and an RNC 211 delivers the MBMS service. Four processes must be performed so that the RNC 211 can provide the MBMS service. The four processes including announcement, joining, notification, and radio bearer (RB) setup processes are sequentially performed.
In the announcement process, the CN 221 announces, to the UEs 201 to 203, when the MBMS service begins. The announcement information includes information indicating which kind of MBMS service begins, information of the time at which the MBMS service is initiated, a service-persistence time period, etc.
In response to the MBMS service announcement of the CN 221, the UEs 201 to 203 requesting the MBMS service transmit joining request messages to the CN 221 at step 231. The joining request messages include service identification codes for specific MBMS services desired by the UEs 201 to 203 contained in a list of MBMS services provided from the CN 221, and identities or identifiers (IDs) of the UEs requesting the MBMS service. For illustrative purposes, all the UEs 201 to 203 illustrated in FIG. 2 request the MBMS service. Therefore, all the UEs 201 to 203 transmit the joining request messages to the CN 221 in step 231.
Upon receiving the joining request messages from the UEs 201 to 203, the CN 221 transmits a joining response message to the UEs 201 to 203 requesting the MBMS service at step 232. The joining response message contains the MBMS service identification codes, IDs of the UEs requesting the MBMS service, key information for MBMS service security, a temporary multicast group identity (TMGI), etc. The TMGI contains a value assigned to the UEs joined for the specific MBMS service. One component contained in the CN generates the value. The generated value is transferred to the UEs making MBMS service requests. Each of the UEs receiving the TMGI receives the MBMS service if the received TMGI matches an MBMS service TMGI. When the above-described operations are terminated, the CN 221 stores information relating to the MBMS service to be provided and information of the UEs 201 to 203 requesting the MBMS service and manages the stored information. That is, the CN 221 generates a service context and manages the generated context. For example, a certain group of information generated, e.g. a certain operation is performed according to the corresponding status or maintenance data.
According to the notification process, the CN 221 notifies the UEs 201 to 203 requesting the MBMS service that the MBMS service will begin. That is, the CN 221 notifies the UEs 201 to 203 requesting the MBMS service through the RNC 211 that the MBMS service will begin via the RNC 211 at step 241. At step 241, the CN 221 notifies the RNC 211 of a list of the UEs 201 to 203 supporting the MBMS service, a list of routing areas (RAs), and the TMGI. Because the RNC 211 supporting the MBMS service and another RNC 211 not supporting the MBMS service are located together in the RAs, the RNC 211 supporting the MBMS service must newly set at least one area in which the MBMS service is supported. Further, the RNC 211 transmits the TMGI to the UEs 201 to 203 that will receive the MBMS service at the above step 241.
The UEs 201 to 203 receiving the TMGI from the RNC 211 transmit notification response messages to the CN 221 at step 242. The response messages contain the TMGI and the IDs of corresponding UEs that will receive the MBMS service.
The radio bearer setup process is performed between the UEs 201 to 203 requesting the MBMS service and the RNC 211. In the radio bearer setup process, radio resources are assigned so that the MBMS service can be provided and relative components are notified of radio resource-related information. The radio bearer setup process is divided into a process for assigning a radio access bearer (RAB) associated with the MBMS service between the CN 221 and the RNC 211 and a process for assigning an RAB associated with the MBMS service between the RNC 211 and the UEs 201 to 203.
MBMS control information necessary for enabling the MBMS service data to be received without any errors is transmitted during the radio bearer setup process. That is, the UEs 201 to 203 can recover the transmitted MBMS service data using the MBMS control information without any errors. When the radio bearer setup process has been completed, all UEs 201 to 203 requesting a specific MBMS service recognize information of a radio link through which the MBMS service is provided and information of a higher layer in which the MBMS service is processed.
If the four processes are performed, the RNC 211 generates, stores, and manages a list of the UEs 201 to 203 receiving the specific MBMS service and information about the specific MBMS service. Furthermore, if the four processes are performed, specific MBMS service data begins to be transferred.
At step 261, the RNC 211 transfers the MBMS data received from the CN 221 to the UEs 201 to 203 requesting the MBMS service. The UEs 201 to 203 recover the received MBMS data using the MBMS control information without any errors. The MBMS control information can be changed while the MBMS service is provided. Further, the changed MBMS control information is contained in an MBMS control signal and the MBMS control signal is transmitted.
The MBMS control information can be changed according to change factors of bearer type switching, mobility management, key management, key management, reconfiguration, etc. For illustrative purposes, the MBMS control information has been changed due to one of the change factors of the MBMS control information in FIG. 2. According to the change of the MBMS control information, the CN 221 transmits the changed MBMS control information to the UEs 201 to 203 receiving the MBMS service. That is, the RNC 211 transmits the MBMS control information received from the CN 221 to the UEs 201 to 203 receiving the MBMS service through the MBMS control signal at step 271. In FIG. 2, the UE #1 201 and UE #M 202 have received the changed MBMS control signal from the RNC 221 without any errors, but the UE #N 203 has not received a changed MBMS control signal or has received an erroneous control signal due to the degradation of a channel environment.
The RNC 211 transmitting the MBMS control signal transfers the MBMS data received from the CN 221 to the UEs 201 to 203 receiving the MBMS service at step 262. In this case, the UE #1 201 and UE #M 202 can recover the MBMS data transferred at the above step 262 using changed MBMS parameters without any error. However, because the UE #N 203 has not received the changed MBMS control information transferred from the RNC 211 at the above step 271, the MBMS data transmitted from the RNC 211 cannot be correctly recovered. If the UE #N 203 does not receive newly changed MBMS control information, there is a problem in that all received MBMS data units are not recovered thereafter. Therefore, a need exist for a method for enabling the changed MBMS control information to be received without any error.
To summarize, a common service can be provided to two or more UEs as in the MBMS service. A UE or a number of UEs may not receive the MBMS control information in a method for transmitting and receiving the MBMS control information. Therefore, an improved method for enabling a UE or the UEs to appropriately receive the MBMS control information is required. Further, there is required a method for recovering from an incurable error when the UE that has not received the MBMS control information recovers the MBMS data using previous information or erroneous control information, although MBMS control information has changed.